In computer graphics, a gradient is a directional change in a feature of an image. A color gradient, for example, is a portion of an image where color gradually changes in a particular direction. Basic gradients have color contours that follow simple paths, such as straight lines or ellipses. Most rendering systems support simple gradients, which allows authoring programs to create them in a resolution-independent way. This allows the final renderer to use the device attributes and output size to assign colors in a way that will avoid banding artifacts, creating a “custom” gradient tailored to the device attributes and output size.
Contour gradients, sometimes called shape gradients, are another type of gradient. Because of their complexity, they are not directly supported by rendering systems. Instead, applications that support them represent them using combinations of simpler constructs, such as raster images or multiple inset copies of a path. Neither of these solutions, however, is resolution or scale independent. Instead, resolution and contour spacing is determined by the authoring program when an illustration is saved. If the results are later scaled up, pixels or contours can become evident.